Active galactic nuclei in low surface brightness galaxies

Weimin Yuan Yunnan Observatory

Based on Master thesis work of Lin MeiIn collaboration with X.B. Dong (USTC)astro-ph/0902.0862

Questions to address

What is the fraction of LSBG that host an AGN?

How the AGN fraction depends on the properties of LSBG?

Low surface brightness galaxies

Disk central surface brightness μ0(B) significantly faint

er than the classical Freeman value μ0(B) ≈21.65mag

arcsec−2

definition: μ0(B) of galactic disk >22-23 mag arcsec−2

(μ(B) of night sky background) A significant constitution of all galaxies in the Universe,

could be over 50% (e.g., Freeman 1970; McGaugh et al. 1995, Bothun et al. 1997)

Comparison with high surface

brightness galaxies (HSBG)

Low star-formation rate Low surface gas density (Auld et al.) Low metallicity, ~1/3 solar (Impey & Bothun 1997)

low dust Rich in HI gas Less evolved system

prevents enrichment of the ISM, prevents cooling and resulting in a less evolved system

Bulges in LSBG

Most LSBG are either bulgeless, late-type "normal-sized" galaxies, or giant galaxies with a significant bulge component

Bulge and disk relation bulge and disk scale length are correlated bulge-to-disk ratio is independent of galaxy type

(Galaz. 2006)

A prototype LSBG: Malin 1

μ0 (B) = 25.5mag arcsec−2

Size >100kpc

HI mass ~1011 Msun

Seyfert nuclear activity (Impey 1989)

Why study AGN in LSBG?

A census of central SMBH in LSBG May provide a complementary clue to understanding

the formation and growth of SMBH As LSBG may have experienced a different route in

the formation and evolution from HSBGfew or no merging history ?

Feedback from powerful AGN may have ecological effects on the evolution LSBG

Hints from comparing AGN properties in LSBG and in HSBG Dependence of AGN activity on host galaxy

properties AGN triggering mechanism

studies of AGN in LSBG --- rare and controversial

Not well studied: only a few cases of secured AGN detections

A high AGN detection rate was ever suggested for LSBG

Sprayberry et al. (1993) found 5 AGN (4 Seyfert1 + 1 Seyfert 2) in 10 giant LSBG Schombert (1998) claimed ~50% of large, HI-rich LSBG have signatures of low-L AGN (based on [NII] and [SII], plus [OI]) But cannot be confirmed by Impey et al. (2001), who found AGN in only <~ 5% LSBG

previous work suffered from problems of: sample: small size, strong biases, etc. low quality data: low R and S/N spectra data analysis: e.g. no proper subtraction of host galaxy light

Sample and data

parent LSBG sample: Impey et al. 1996 UK Schmidt survey plate scanned by APM 693 LSBG within 786 sqr.deg. in the local universe (z

<0.1) largest and homogeneous LSBG sample in northern s

ky our sample: spectroscopically observed in SDSS DR5

194 LSBG comparative HSBG sample:

need reliable morphological classification and matching distributions in distances, magnitudes, etc.

3rd Reference Catalogue of Bright Galaxies (RC3) (de Vaucouleurs et al. 1991) --- a catalogue of typical HSBG 142 HSBG with SDSS spectra

SDSS-APM LSBG sample and comparative HSBG sample

Compatible at z<0.04

Analysis of SDSS spectra

Using the algorithm developed by Tinggui Wang’s group at USTC (Zhou et al. 2006)

Spectral decomposition: AGN + host galaxy Self-consistent modeling of host stellar spectrum and AGN

(emission line + continuum) spectrum (Lu et al. 2006) Spectral fitting (Dong et al. 2005, zhou et al. 2006)

de-blending of broad and narrow emission lines Also available: stellar velocity dispersion σin the central

part (bulge) of the galaxy (by modeling stellar absorption features)

Example of AGN found in LSBG:broad line (type1) AGN in SDSS J122912.9+004903.7

Original SDSS spectrum

stellar spectrum

AGN continuum

AGN emission lines

Broad Ha

Narrow Ha

[NII]

Example of AGN found in LSBG:narrow line (type 2) AGN

Spectral classification of emission line nuclei: AGN vs. star-formation

A significant fraction (~50%) of LSBG have ongoing central star-formation

fraction ofemission line galaxies ~ 68%

AGN

starformation

Kewley et al. 2001

Kauffmann et al. 2003

AGN= Seyfert+ LINER + transition

Spectral classification of emission line nuclei: Seyfert vs. LINER

We regard LINER as powered by AGN

Kewley et al. 2006

Demography of nuclear activity in LSBG

The AGN fraction is lower than 40% found for HSBG in the local universe (Ho 1997)

AGN found across morphological types for LSBG

AGN fraction

• Lower for later types of galaxies

• but significantly higher for interacting galaxies• the same as HSBG

All emission line LSBG

Star-formation nuclei

AGN

Comparison with HSBG at z<0.04

comparative HSBG sample LSBG sample at z<0.04

All emission line galaxies

nuclearStar-formation

AGN

Conclusion: LSBG have a smaller AGN fraction than HSBG, and a comparable or even higher fraction of nuclear star-formation

robust results: the same data set and analysis algorithm

47% consistent with the result of Ho (1997)

Dependence of AGN fraction on size of galaxy

physical size of galaxies (kpc)

AGN tend to reside in galaxies of larger size

AGN fraction

Dependence of AGN fraction on central stellar velocity dispersion

Central stellar velocity dispersion

AGN tend to reside in galaxies with larger central σ For both LSBG and HSBG

LSBG HSBG

AGN fraction in LSBG depends on size of galaxy central stellar velocity dispersion ( of bulges)

Since bulge and disk scale length are correlated (Galaz. 2006), galaxies with more massive bulges have a higher AGN fraction consistent with result for general AGN (e.g.Kauffmann et al. 2003) Reason for different AGN fraction btw. LSBG/HSBG: they occupy different parts of the bulge distribution for given mo

rphological types of galaxies LSBG: lower end of bulge distribution low AGN chance HSBG: higher end of bulge distribution high AGN chance But possibly not due to disk surface brightness

hinted from observations but should be tested explicitly

What causes the difference in AGN fraction between LSBG and HSBG?

Some properties of AGN in LSBG

Vast majority are weak, low-luminosity AGN L[OIII]<1040erg/s

Less dust extinction than HSBG nuclei, based on Balmer decrement of narrow lines, for both AGN and nuclear HII

Lower electron density of narrow line region than that of HSBG AGN ([SII]6717/[SII]6731 line ratio)

Both types found, radio-loud (~20%) and radio-quiet

Kinematics of NLR

The same as AGN in normal HSBG, the kinematics of NLR traces well the galactic bulge potential

Cen

tral

ste

llar

V

disp

ersi

on

Width of narrow line ([NII])

black hole growth in LSBG

3 LSBG AGN with detected broad Ha emission line

Bla

ck h

ole

m

ass

Central stellar V dispersion

Tremaine et al. (2002)

HSBG with AGN follow the well known M-σ relation for normal galaxies

Is SMBH-galaxy co-evolution also happening in LSBG?How do black holes grow in LSBG? More data are needed!

M-σ relation

conclusion I -- demography of nuclear activity in LSBG

Emission-line nuclei are common (68%), mostly star-forming nuclei (52%)

Similarity to HSBG: AGN found in a wide range of morphological types from Sa

to latter types. Interacting galaxies have the highest fraction AGN tend to reside in galaxies with larger/massive bulges

difference in AGN fraction btw LSBG and HSBG Overall fraction of AGN in LSBG is ~15%, smaller than

~40% for normal HSBG may be due to different bulge distribution for the same

morphological type likely NOT due to the difference in disk surface brightness

conclusion II -- AGN properties

some similar properties to AGN in HSBG NLR kinematics traces well the bulge gravitational potential Both radio-loud and radio-quiet (similar fraction)

Differences from AGN in HSBG Less nuclear dust extinction lower electron density of NLR

More data are needed to constrain BH and bulge growth in LSBG

Questions raised

How do SMBH grow in LSBG, which experience little or no merging?

Are all SMBH grow via galaxy merging?

Next step

Deep imaging of LSBG for bulge/disk decomposition (using the YNAO Lijiang 2.4m)

Distribution of black hole mass and Eddington ratio Better constraint to the BH growth and M-σrelation for L

SBG Select new LSBG samples from SDSS and other imagi

ng survey data

Thank you for your attention